Sound Power and Intensity Level

Decibels are often used as absolute measurements, with one of the quantities being a fixed reference.

The sound power level

$\displaystyle L_W = 10\log W/W_0$ dB $\displaystyle ,$

and sound intensity level

$\displaystyle L_I = 10\log I/I_0$ dB $\displaystyle ,$

of a source, may be expressed using the threshold of audibility as a reference, defined by

$\displaystyle W_0$	$\displaystyle =$	$\displaystyle 10^{-12}$ W $\displaystyle ,$
$\displaystyle I_0$	$\displaystyle =$	$\displaystyle 10^{-12}$ $\displaystyle \mbox{ W/m$^2$}$ $\displaystyle .$

``Music 270a: Fundamentals of Audio, Acoustics and Sound'' by Tamara Smyth, Department of Music, University of California, San Diego (UCSD).